Lighting up the Electrochemiluminescence of Carbon Dots through Pre- and Post-Synthetic Design

Carbon dots (CDs), defined by their size of less than 10\ua0nm, are a class of photoluminescent (PL) and electrochemiluminescent (ECL) nanomaterials that include a variety of carbon-based nanoparticles. However, the control of their properties, especially ECL, remains elusive and afflicted by a series of problems. Here, the authors report CDs that display ECL in water via coreactant ECL, which is the dominant mechanism in biosensing applications. They take advantage of a multicomponent bottom-up approach for preparing and studying the luminescence properties of CDs doped with a dye acting as PL and ECL probe. The dependence of luminescence properties on the surface chemistry is further reported, by investigating the PL and ECL response of CDs with surfaces rich in primary, methylated, or propylated amino groups. While precursors that contribute to the core characterize the PL emission, the surface states influence the efficiency of the excitation-dependent PL emission. The ECL emission is influenced by surface states from the organic shell, but states of the core strongly interact with the surface, influencing the ECL efficiency. These findings offer a framework of pre- and post-synthetic design strategies to improve ECL emission properties, opening new opportunities for exploring biosensing applications of CDs

Electrodes Modified with Poly(3,4-Ethylenedioxythiophene) Doped with Sulfonated Polyarylethersulfones: Towards New Conducting Polymers

To overcome the well-known technical problems of Poly(3,4-Ethylenedioxythiophene) (PEDOT), i.e. difficult processability and patterning, due to its poor solubility in common organic and inorganic solvents, PEDOTs characterized by a full miscibility in the reaction solvents used, were successfully synthesized by a direct oxidative polycondensation reaction between Ethylenedioxythiophene (EDOT) and an oxidant species, i.e. ferric sulfate, in four organic reaction solvents: N, N-dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP). The oxidative polycondensation of EDOT in the presence of Sulfonated Polyarylethersulfone (SPAES) as doping agent characterized by three increasing degree of sulfonation (DS), i.e. 0.5, 0.75 and 1.0 (meq SO3-\ub7g-1 of polymer), was performed for the first time, leading to a new conducting material: PEDOT_SPAES. PEDOT_SPAES can be easily processed and casted onto the surface of glassy carbon electrodes, reaching better electrochemical performances with respect to the precursors. PEDOT_SPAES chemical structure was investigated via wide-angle scattering (WAXS): comparing WAXS spectra of unmodified PEDOT and commercial PEDOT doped with 2-Naphthalenesulfonic acid, having crystalline structures, with the spectra of PEDOT_SPAESs, that are characterized by amorphous structures, it is possible to assess that for the first time PEDOT-based materials doped with SPAES were synthesized

A Combined XRD, Solvatochromic, and Cyclic Voltammetric Study of Poly (3,4-Ethylenedioxythiophene) Doped with Sulfonated Polyarylethersulfones: Towards New Conducting Polymers

Despite the poor solubility in organic solvents, poly (3,4-ethylenedioxythiophene) (PEDOT) is one of the most successful conducting polymers. To improve PEDOT conductivity, the dopants commonly used are molecules/polymers carrying sulfonic functionalities. In addition to these species, sulfonated polyarylethersulfone (SPAES), obtained via homogeneous synthesis with different degrees of sulfonation (DS), can be used thanks to both the tight control over the DS and the charge separation present in SPAES structure. Here, PEDOTs having enhanced solubility in the chosen reaction solvents (N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone) were synthesized via a high-concentration solvent-based emulsion polymerization with very low amounts of SPAES as dopant (1% w/w with respect to EDOT monomer), characterized by different DS. The influence of solvents and of the adopted doping agent was studied on PEDOT_SPAESs analyzing (i) the chemical structure, comparing via X-ray diffraction (XRD) the crystalline structures of undoped and commercial PEDOTs with PEDOT_SPAES\u2019 amorphous structure; (ii) solvatochromic behavior, observing UV absorption wavelength variation as solvents and SPAES\u2019 DS change; and (iii) electrochemical properties: voltammetric peak heights of PEDOT_SPAES cast onto glassy carbon electrodes differ for each solvent and in general are better than the ones obtained for neat SPAES, PEDOTs, and glassy carbon

Insights into the mechanism of coreactant electrochemiluminescence facilitating enhanced bioanalytical performance

Electrochemiluminescence (ECL) is a powerful transduction technique with a leading role in the biosensing field due to its high sensitivity and low background signal. Although the intrinsic analytical strength of ECL depends critically on the overall efficiency of the mechanisms of its generation, studies aimed at enhancing the ECL signal have mostly focused on the investigation of materials, either luminophores or coreactants, while fundamental mechanistic studies are relatively scarce. Here, we discover an unexpected but highly efficient mechanistic path for ECL generation close to the electrode surface (signal enhancement, 128%) using an innovative combination of ECL imaging techniques and electrochemical mapping of radical generation. Our findings, which are also supported by quantum chemical calculations\ua0and spin trapping methods, led to the identification of a family of alternative branched amine coreactants, which raises the analytical strength of ECL well beyond that of present state-of-the-art immunoassays, thus creating potential ECL applications in ultrasensitive bioanalysis

Electrochemiluminescence as emerging microscopy techniques

The use of electrochemiluminescence (ECL), i.e., chemiluminescence triggered by electrochemical stimulus, as emitting light source for microscopy is an emerging approach with different applications ranging from the visualization of nanomaterials to cell mapping. In this trend article, we give an overview of the state of the art in this new field with the purpose to illustrate all the possible applications so far explored as well as describing the mechanism underlying this transduction technique. The results discussed here would highlight the great potential of the combination between ECL and microscopy and how this marriage can turn into an innovative approach with specific application in analytical sciences. [Figure not available: see fulltext.]

Poly(3,4-Ethylenedioxythiophene) (PEDOT) polymers doped with Sulphonated Polyarylethersulphones for electroanalytical applications

Among Polythiophene derivates, Poly(3,4-Ethylenedioxythiophene) (PEDOT) is one of the most successful conducting polymer due to its excellent environmental stability and high electrical conductivity. Numerous researches have been conducted on PEDOT synthesis by electrochemical and chemical polymerization of 3,4-Ethylenedioxythiophene (EDOT). Chemical approaches, performed by high-concentration water-based emulsion polymerization of EDOT, produce PEDOT precipitates as dark-blue powders, which are insoluble in water [1]. To improve PEDOT solubility and conductive properties, PEDOT polymers can be doped with sulphonated dopants, the most commonly used being 2-Naphthalenesulphonic acid and para-toluene sulphonic acid, which however yield to scarce possibility to modify and tailor the properties of the final materials. Anyway, as already shown in previous investigations, electrodes modified with SPAES (e.g. deposited on glassy carbon supports) demonstrated to possess good electrochemical performances in terms of higher analyte currents, strongly dependent from the casting solvent [2] and on the ion exchange capacity (IEC). In this context, in the present work, Sulphonated Polyarylethersulphone (SPAES) polymer, synthesized via homogeneous synthesis with different IEC [3], is proposed as new doping agent, allowing both a tight control over the IEC and a charge separation already present in SPAES structure, deriving from the pre-sulphonated comonomer [3,4]. PEDOT doped with SPAES is synthesized via a high-concentration solvent-based emulsion polymerization of EDOT in four different reaction solvents (N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide and N-methyl-2-pyrrolidone). Bare SPAES, bare PEDOT and PEDOT doped with 2-Naphthalenesulfonic acid are also synthesized for comparison. Despite the very low amount of SPAES used (1% w/w respect to EDOT), PEDOT_SPAES appears to be a material very different from its original components. For instance, wide-angle scattering (WAXS) measurements show how the crystalline structure of bare PEDOT or PEDOT doped with 2-Naphthalenesulfonic acid is lost, with an increase of the amorphous phase when SPAES is added as doping agent. These new materials, when used as electrode modifiers, yield to an increase in the general electroanalytical performances, in terms of higher peak currents (with respect to the Ru probe). In particular, the type of casting solvent appears to be an important parameter for the modulation of the adhesion, homogeneity and porosity of the polymeric membrane on the electrode surface and consequently of the electrochemical signal. The electrochemical investigation demonstrates also the importance of other variables, such as IEC, stabilization time, drying temperature and pressure, to assure a good electrode response. Therefore, a Principal Component chemometric Analysis is also employed for results rationalization. References [1] Y. Lei, H. Oohata, S. Kuroda, S. Sasaki and T. Yamamoto, Synth. Met. 149 (2005) 211-217. [2] L. Falciola, S. Checchia, V. Pifferi, H. Farina, M.A. Ortenzi, V. Sabatini, Electrochim. Acta 194 (2016) 405-412. [3] V. Sabatini, S. Checchia, H. Farina, M. A. Ortenzi, Macromol. Res. 483 (2016) 285-291. [4] V. Sabatini, H. Farina, M. A. Ortenzi, Polym. Eng. Sci. 57 (2017) 491-501

Electrodes Modified with Poly(3,4-Ethylenedioxythiophene) Doped with Sulfonated Polyarylethersulfones: Towards New Conducting Polymers

To overcome the well-known technical problems of Poly(3,4-Ethylenedioxythiophene) (PEDOT), i.e. difficult processability and patterning, due to its poor solubility in common organic and inorganic solvents, PEDOTs characterized by a full miscibility in the reaction solvents used, were successfully synthesized by a direct oxidative polycondensation reaction between Ethylenedioxythiophene (EDOT) and an oxidant species, i.e. ferric sulfate, in four organic reaction solvents: N, N-dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP). The oxidative polycondensation of EDOT in the presence of Sulfonated Polyarylethersulfone (SPAES) as doping agent characterized by three increasing degree of sulfonation (DS), i.e. 0.5, 0.75 and 1.0 (meq SO3-\ub7g-1 of polymer), was performed for the first time, leading to a new conducting material: PEDOT_SPAES. PEDOT_SPAES can be easily processed and casted onto the surface of glassy carbon electrodes, reaching better electrochemical performances with respect to the precursors. PEDOT_SPAES chemical structure was investigated via wide-angle scattering (WAXS): comparing WAXS spectra of unmodified PEDOT and commercial PEDOT doped with 2-Naphthalenesulfonic acid, having crystalline structures, with the spectra of PEDOT_SPAESs, that are characterized by amorphous structures, it is possible to assess that for the first time PEDOT-based materials doped with SPAES were synthesized

Sodium bis(2-ethylhexyl)sulfosuccinate self-aggregation in vacuo: molecular dynamics simulation

Molecular dynamics (MD) simulations were conducted for systems in vacuo consisting of n AOT anions (bis(2-ethylhexyl)sulfosuccinate ions) and n 1 or n Na+ ions up to n = 20. For n = 15, positively charged systems with Li+, K+, and Cs+ cations were also considered. All systems were observed to form reverse micelle-like aggregates whose centre is occupied by cations and polar heads in a very compact solid-like way, while globally the aggregate has the form of an elongated and rather flat ellipsoid. Various types of statistical analyses were carried out on the systems to enlighten structural and dynamical properties including gyration radius, atomic pair correlation functions, atomic B-factor and moment of inertia tensor. For completeness and comparison the stability of reverse micelle is tested in the case of neutral n = 20 system in CCl4 solution

Electrochemiluminescent immunoassay enhancement driven by carbon nanotubes

Electrochemiluminescence (ECL) is a leading analytical technique for clinical monitoring and early disease diagnosis. Carbon nanotubes are used as efficient nanomaterials for ECL signal enhancement providing new insights into the mechanism for the ECL generation but also affording application in bead-based immunoassay and ECL microscopy-based bioimaging